Computing and communication networks typically include devices, such as routers, switches or gateways, which transfer or switch data, such as packets, from one or more sources to one or more destinations. A packet is a structure that encapsulates data for transmission through a network based on control information that is stored in a header portion of the packet. A router is a switching device that can receive a packet and, based on the packet header, may forward the packet towards its final destination.
A firewall is a device that inspects network traffic passing through it, and may perform actions, such as denying or permitting passage of the traffic based on a set of rules. Firewalls may be implemented as stand alone network devices or, in some cases, integrated in a single network device, such as a router or switch, which performs other functions. For instance, a network switch may perform firewall related functions as well as switching functions.